This invention relates generally to a method of controlling an automated clutch to prevent engine stall in a motor vehicle equipped with an automated clutch.
There is a current and growing interest to increasingly automate the function of a motor vehicle driveline in an effort to increase efficiency in operation. This need for efficient use of engine power during all conditions is of increasing interest to manufacturers and consumers of large trucks.
It is known to use an automated clutch system that actuates a clutch in the same manner as a manual clutch. Typically, an automated clutch system includes a clutch selectively engaged to a flywheel to transmit power from the motor to the transmission, and a control system to actuate the clutch. The automated clutch system includes a friction disk that selectively engages a flywheel driven by the engine. An automated clutch system duplicates the actions of a skilled and experienced operator to optimize operation, such as gear changes, of the motor vehicle.
A motor vehicle equipped with an automated clutch system does not include a clutch pedal for manual actuation of the clutch; instead, a controller controls actuation of the clutch to facilitate gear changes. As appreciated, there are other instances beside gear changes that require disengagement of the clutch from the flywheel. The controller is therefore programmed to disengage the clutch during other conditions. One of these conditions is during coasting of the motor vehicle. Coasting defines a condition when the motor vehicle is moving and the throttle pedal is not engaged, such as when approaching a stop light or slowing for traffic. Typically, when a coasting condition is detected, the controller will proportionally open the clutch to prevent the engine from stalling and provide a smooth transition to a slower speed. However, if an operator is engaging the accelerator the controller will not detect that the motor vehicle is coasting to open the clutch. Therefore, the control does not open the clutch in situations such as panic stops where an operator may be pressing both the accelerator and the brake pedal.
Further, large trucks typically includes engines of such power that they can drive through the brakes. In other words, the engine can overpower the brakes and result in continued movement when the need is to stop quickly, or can result in the engine stalling.
Another condition causing stalling of the engine includes an unexpected stop, for instance when approaching a traffic light that unexpectently changes sooner than anticipated. As appreciated, the motor vehicle with an automated clutch would typically detect a coasting condition and proportionally open the clutch to account for slowing of the vehicle. However, in some instances, an inexperienced operator may rest a foot on the throttle pedal to exert sufficient pressure such that a coasting condition is not detected and the clutch will remain closed, causing undesirable engine stall.
Large truck manufacturers and fleet operators are constantly seeking ways to improve efficiency and reduce costs. Operating a large truck at or near engine stall conditions places great stress on the motor vehicle and in some instances can cause damage to the engine. Increased stress on the engine can increase maintenance and operating costs of the motor vehicle.
Such automated clutches utilized in automatic transmissions and in so-called assisted manual type transmissions wherein part of the manual shifting process is assisted by automated controllers, such as an automated clutch. The present invention would have benefits in automated clutches utilized with either type transmission.
For these reasons, it is desirable to design an automated clutch control system that opens the clutch in response to potential stall conditions with the throttle pedal actuated.
An embodiment of this invention is a system and method of controlling an automated clutch system to prevent engine stall by detection of motor vehicle conditions indicative of engine stall.
The automated clutch system for a motor vehicle includes an engine coupled to a transmission by way of an automated clutch. The automated clutch includes a friction element for selective coupling to a flywheel driven by an engine output shaft. The automated clutch actuates to open the connection between the engine and transmission to facilitate gear changes. A disclosed controller operates the automated clutch in either a manual or automatic mode. In the manual mode, the controller actuates the automated clutch in response to operator input through the gearshift lever, much like normal operation of a manually shifted transmission. Alternatively, the controller can operate the automated clutch in concert with the transmission to automatically shift gears in response to specific engine speed and vehicle acceleration conditions. The specifically disclosed controller is utilized in one type of transmission which combines both the assisted manual shifting and the automatic shifting options as described above. However, then again as mentioned above, this invention would cover not only this disclosed embodiment, but also either of the separate transmission types.
The controller accommodates coasting by opening the clutch in proportion to the speed of the vehicle. The proportional opening of the clutch reduces the amount of contact between the friction plate and the flywheel to allow a predetermined amount of slipping. Coasting is a condition where there is no accelerator pedal input, but the vehicle is still moving, such as slowing for a traffic light or for slower vehicles. The controller detects a coasting condition only in the absence of accelerator pedal input, therefore, if an inexperienced operator errantly rests his foot on the accelerator pedal, the controller will not detect a coasting condition to open the clutch. Further, during a panic stop where an operator actuates both the brake and the accelerator the clutch will not open. This invention is a method of detecting conditions indicative of engine stall and proportionally opening the automatic clutch in response to engine stall conditions even when the accelerator pedal is actuated.
The method includes the initial step of determining an engine stall threshold relative to current operating conditions of the motor vehicle. The engine stall threshold includes correction factors for vehicle acceleration and for the time at a predetermined engine speed. The engine speed threshold value is the engine speed at which the clutch will open proportionally to prevent the engine from stalling. An engine speed below the engine speed threshold value will prompt a check by the controller of vehicle acceleration. If the vehicle is accelerating sufficiently to prevent engine stall, even at lower engine speeds, the controller will not open the clutch.
Once it is determined that current engine speed is below the engine speed threshold, and motor vehicle acceleration is below a predetermined threshold, the controller will actuate the clutch to selectively couple the engine and transmission to prevent engine stall.
An on/off check is included in the system to allow inclusion of the stall prevention control within the much larger clutch control system such that the stall prevention control portion can be selectively engaged according to the specific configuration of the motor vehicle.
Additionally, a check for engagement of the foot brake before actuating the automatic clutch is conducted. Engagement of the foot brake is a requirement for the controller to actuate the clutch in one embodiment of this method. Another embodiment of this method does not require actuation of the foot brake to allow the clutch to open.
The controller maintains proportional clutch opening until a clearing condition is detected. The clearing conditions are conditions of the vehicle that indicate that engine stall should be allowed, or that engine stall has been prevented by actions other than engine stall control. The controller continues to proportionally open the clutch until one of the clearing conditions is detected so that the controller resumes normal operation of the automatic clutch.
The automated clutch control system of this invention detects stall conditions and properly actuates the clutch to prevent the engine from stalling to simplify the operation of a motor vehicle equipped with an automated clutch.